1. Field of the Invention
The field of the invention is in the mechanisms and/or methods for defeating, removing, or reducing the effects of the video copy protection signals. These mechanisms are also used to synthesize and improve the performance of a video copy protection signal.
2. Description of the Prior Art
The Hollywood movie industry is very concerned about the unauthorized copying of movies and programs. As an example, on Sep. 17, 1997 Jack Valenti, President and Chief Executive Office of the Motion Picture Association of America stated “If you can't protect what you own—You don't own anything.” The U.S. Pat. No. 4,631,603, by Ryan, incorporated by reference, discloses a way to process an ordinary program video source to have copy protection. The copy protected video is viewable on a TV set but it produces a recording lacking any entertainment value. That is, the video programs that are not recordable suffer from artifacts ranging from low contrast to synchronizing problems. The '603 patent describes a method for “confusing” or causing misoperation of the AGC system in a videocassette recorder while not causing a black depression problem in a television receiver displaying the copy protected signal.
A Polish Patent Application (PL 304477 ('477)) by Tomasz Urbaniec entitled “Method and Device for Protecting Videophonic Recordings Against Unauthorized Copying” filed Jul. 28, 1994, hereby incorporated by reference, discloses a variation of the '603 patent by Ryan. FIG. 1a of the '603 patent describes the waveform of the copy protected video signal as disclosed by Ryan and is replicated herein as FIG. 1a. FIG. 4 of the Urbaniec patent '477 describes the comparative waveform as disclosed by Urbaniec, which is replicated herein as FIG. 1(b).
As is well known in the art, the videocassette system has a limited luminance frequency response, less than 2 MHz. A signal as described by Ryan recorded on a videocassette duplicating recorder with the AGC turned off (to avoid the effects of copy protection) will produce a video signal with pulse shapes modified by the limited frequency response of the duplicating recorder. Since there is no gap between the pseudo sync pulses and the AGC pulses of Ryan, the AGC system of a home duplicating recorder will respond to the combination of the pseudo sync pulses and the AGC pulses.
The limited bandwidth of the recording VCR responds slightly differently to the combination of pseudo-sync and AGC pulses separated by a time gap of 0.5 μseconds to 2.0 μseconds. If the time gap is as low as 0.5 μseconds, the limited bandwidth of the recording videocassette recorder distorts the time gap to effectively remove it and the effectiveness of the copy protection is essentially the same as that achieved by Ryan. As the gap widens, the effectiveness of the copy protection is reduced or removed.
To defeat the copy protection process, there are a number of known ways such as attenuating, blanking, narrowing, level shifting, modifying and/or clipping the copy protection pulses as described in U.S. Pat. Nos. 4,695,901 ('901), 4,336,554 ('554), 5,157,510 ('510), 5,194,965 ('965), 5,583,936 ('936), 5,633,927 ('927), 5,748,733 ('733) and 5,661,801 ('801) cited above and hereby incorporated by reference.
In the patents mentioned above, the AGC and/or sync or pseudo sync pulses (see U.S. Pat. No. 4,695,901) are changed in amplitude, changed in level relative to normal sync pulses, and/or changed in pulse width, so as to allow a satisfactory recording.
In particular, U.S. Pat. Nos. 5,194,965 and 5,157,510 disclose narrowing of the AGC and/or pseudo sync pulses so that the record VCR does not sense these narrowed added pulses and thus, makes a satisfactory copy.